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hawk300bg

Grob 109 mechanic

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hawk300bg

Help !  I am the owner of a Grob 109 motor glider and need a mechanic who is familiar with the pitch change mechanism and how to diagnose and fix the problem.  The prop is stuck in cruise pitch and will not return to climb pitch. I am based at DYL just outside of Philadelphia, PA.  I am looking to hire a mechanic to fix the problem, I will also pay expenses to get to DYL.

Rich Kochanski 

N300BG

call or text me at 215 738-9253

email hawk300bg@gmail.com

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bberson

On the ground, did you try twisting the blades to release the high pitch catch tab on the prop?

Do that before every flight.

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hawk300bg

I did but it did not work.  I realize that should put the prop in climb pitch but it did not.  Still cannot get more than 2400 rpms.  I’ve checked the prop with an optical tach and it agrees with the instrument tachometer.  Not sure what next.  Have you ever had a problem with the pitch change mechanism ?

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StuOstrander

I have responded directly to Rich. We're going to talk (phone) later today. I first provided this:

The pitch change mechanism is relatively simple when you study it the least little bit. Before you pay for a mechanic, I would encourage you to take a look at it yourself. The solution might be simply lubricating the sliding components.

          Remove the spinner and you will be able to see the components that you can readily, and legally clean and lubricate yourself.

          Attached is a link to (4) very short videos showing the pitch change unit on the work bench in Tim Dews’ shop in England. Tim is demonstrating to Ron Schweninger (Grob G109B N109BR) how the pitch change mechanism works.

          If you watch these (particularly 02 Prop) a few times and then look at your own mechanism, you will understand how the pitch change mechanism works.

          The manual explains the operation of the mechanism, but “a picture is worth a thousand words”. And when you can see it and touch it, it is worth ten thousand words.

          Let me also try to explain it in my words:

-       When you pull the pitch change handle in the cockpit, the prop is pushed forward on its shaft.

-       As the prop moves forward, the pitch of the prop blades is increased.

-       A small plate is spring loaded to be held in a “centered” position on the prop shaft. This plate is illustrated very clearly at the beginning of  the 02 Prop video.

-       As rpm is increased, a point is reached where centrifugal force overcomes the spring force and the plate will slide to the cruise position (when the prop is moved forward)

 

I think this sliding plate is where you need to look. It may not be

returning to the “centered” position which allows the prop to return to climb position. The plate should slide back and forth easily when you move the prop forward.

-       Are the surfaces clean?

-       Are the plastic guides in place?

-       Is the plate damaged in anyway?

 

I recommend you make those checks before you call a mechanic. Not

all AP’s are going to be familiar with the Hoffman Prop. It isn’t exceptionally complex, but neither is it something most AP’s ever see.

          https://www.dropbox.com/sh/48piq11758xa8p1/AADyXBJ5o87Iq4-JWQpZjypla?dl=0

 

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